Anemometry devices for measuring wind speed by exposure of an electrically heated element to air flow are known. For example devices have been used in wind tunnels comprising a wire suspended between upstanding terminals. The wire is electrically energised and is mounted in a bridge circuit to monitor changes of resistance arising from changes in temperature of the element (via the temperature coefficient of resistance) when the wind speed changes. However such devices are not suitable for an aircraft in service, since they are fragile. In order to measure the wind speed of an aircraft, a device is required that is resistant to knocks and abrasions.
It has been proposed to employ MEMS hot film sensors applied to an aircraft fuselage, which include a titanium layer serving as a heating element, mounted on a polyimide layer—see FIG. 9 of Warsop, C.: “AEROMEMS—An Investigation into the Viability of MEMS Technology for Boundary Layer Control”; presented at the American Institute of Aeronautics and Astronautics (AIAA) Applied Aerodynamics Conference, held in Norfolk, Va., USA; AIAA paper No. AIAA-99-3173; June 1999. However, such proposal was at an initial stage of development, and further improvements are desirable.